Process for the production of pulp from bagasse



Edward L. Powell, Lookout Mountain,

No. 188,265, filed October 3, 1950,

United States Patent PROCESS FOR THE PRODUCTION OF PULP FROM BAGASSETenn., assignor to grown and Root, Inc., Houston, Tex., a corporation ofexas 1 No Drawing. Application February 25, 1953 SEl'lfllNO. 338,910

2 Claims. (Cl. 162-58) The present invention relates to processes forproducing purified cellulose for chemical consumption and moreparticularly is directed to the production of pulp from bagasses for useas chemical pulp, paper pulp and the like in subsequent manufacturingprocesses. This application is a continuation in part of my applicationSerial entitled Process for the Production of Bulk From Bagasse, nowabandoned.

Presently available sources of raw materials for the production of pulpinclude wood, straw and cotton linters. Due to the large volume of pulpnow being used industrially, these sources are rapidly becominginadequate and it has become necessary to find new sources of rawmaterials. One such source, which is readily available in amplequantities,is the bagasse which is a necessary waste product in theproduction of sugar from sugar cane. Bagasse is present in many areas ofthe World, chiefly in the tropical and lower temperate zones. Since itis a waste product and is available throughout the world in largequantities, it constitutes a fruitful new source of pulp, where its useas a fuel can, if necessary, be partially or completely replaced by moreconventional fuels.

Bagasse results from the crushing of sugar cane in the production ofsugar, in which the cane is shredded and the shreds are passed betweenheavy rolls for squeezing out the saccharine juices from the planttissues. The residue resulting from the sugar extraction process is acoarse, fibrous mass which is commercially known as bagasse and hasgenerally been used as a fuel burned in the steam boilers of the sugarplantations.

The treatment of bagasse to render its fibers suitable for use as acommercial pulp must vary, depending primarily upon the end use to bemade of the product.

The bagasse consists essentially of plant tissue containing cellulosefibers, as well as hemicelluloses, pentosans, pectins and gums. Thechemical analysis of bagasse is given on page 171 of The ChemurgicDigest for May 31, 1945. To provide a purified cellulose suitable as acommercial pulp, these hemicelluloses or non-cellulosic components ofthe bagasse may be present in very small amounts or may be removedentirely from the fibers. For this purpose, known processes have treatedthe bagasse fibers at some stage during processing with mineral ororganic acids, but these processes have been proven to be costly tocarry out and theresulting pulp cannot economically compete with otherless expensive pulps, particularly wood pulp made from southern pine.

It is, therefore, one object of my invention to produce a commercialpulp from bagasse, and particularly a pulp which can be'produced at avery low cost, making the pulp commercially desirable.

Another object of my invention is to produce a purified cellulose frombagasse without employing inorganic or organic acids, the process beingcarried out economically, producing a pulp with a low mineral contentand characterized by the high whiteness of its appearance.

A further object is ,to provide a process for the production ofpulp-from bagasse in which the bulk of the incrustants present in thebagasse are removed from it by steam distillation, rather than by analkaline treatment.

Still another object of my invention is to provide a process for theproduction of pulp from bagasse including a pre-hydrolysis treatment ina cooking vessel under steam pressure, a partial venting of the cookingvessel to effect steam distillation of incrustants from the bagasse,followed immediately by an alkaline extraction without completelyremoving the steam pressure and without washing the bagasse between thepre-hydrolysis and the alkaline extraction steps.

The foregoing and other objects, features and advantages of thisinvention will be apparent from the following description, it beingunderstood that the detailed description is merely illustrative of theinvention, which is defined in the claims.

In carrying out the process, relatively long fibered fractions ofbagasse are selected and are separated from the pith and from the shortfibers of the crushed sugar cane by such known processes as wetshredding, dry shredding, flotation, or screening of the coarse fibrousmass of crushed cane. In this manner, the selected fibers, which formabout 50% of the entire mass, are obtained. The selected fibers arepartially fibrillated, as distinguished from relatively coarse bundlesof the crushed cane mass. The bagasse fibers so selected have a moisturecontent of 75% or below.

The depithed, long fibers just described result in a product of aquality slightly higher than that obtained in using whole bagasse. Theyare used to advantage in producing pulp in geographical areas in whichthe rest of the bagasse, including the pith and. the short fibers, isneeded for use as fuel.- 7

On the other hand, in areas where fuelis more readily available and ischeaper, all of the bagasse can be used in producing pulp, with aconsequent higher yield.

Because bagasse fiber is a very bulky material, it was discovered that,to produce an economical return, it would be necessary to use eitherponderous equipment or very rapid processing cycles. In order to avoidthe use of very heavy and expensive equipment, it was deemed morepractical to accelerate the processing cycles. It was found that thiscan be done by using a rotary digester as the cooking vessel, whichmakes possible the use of a lower liquor-to-fiber ratio. As aconsequence, the time and the quantity of heat required to bring thevessel up to pressure are much lower than would otherwise be the case.Such a rotary vessel must be one capable of steam operating pressures upto'150 pounds per square inch.

The bagasse, either in the form of whole bagasse or of depithed fibers,is placed in the cooking vessel, which is then closed and rotated. Livesteam is introduced into the vessel until the proper pressure, about top.s.i, is reached. The vessel is rotated continuously for a period ofabout thirty minutes to one hour, during which time the steam pressureis maintained. The latent acidity of the vapors created is sufficient toeffect the required degree of prehydrolysis.

The rotation of the vessel is stopped and it is then partially venteddown to a pressure of between 50 and 60 p.s.i. During this partialventing or blow-oil, substantially all of the liquefied incrustants areremoved by an effective steam distillation. Although under somecircumstances it may be desirable to vent the vessel completely, it isnot considered essential to do so. With only a partial venting,considerable time may he saved in the whole pulp production cycle.

Under the conditions of this process, in which no actual mineral, orother acid is added it is not necessary to wash the fiber between thepre-hydrolysis treatment and assaeoo the alkaline extraction step. This,also, saves time in the process and, in addition, saves materialbecause, in any washing process, there is'necessarily some loss ofmaterial. Yield values have been consistently higher in the use of myprocess than in the use of other'methods, largely due to the eliminationof the use of applied acids and of this washing step.

After the .vessel'has been vented down to the lower pressure, a caustic,such as-a2 .or' 3% solution of sodium, potassiumor calcium hydroxide, ina weight ratio of 5 to 1, based on the weight of the fiberas originallyplaced in the vessel, is pumped into thevessel under the necessarypressure. Introducing the caustic into the same vessel under pressurefurther shortens the time cycle, since it is not then necessary to buildthe steam pressure up again all the way from atmospheric pressure. Ofcourse, where the vessel has beencompletely vented, such pressure on thecaustic is not needed. Rotation of-the vessel 'is begun again and steamis introduced into the vessel to a pressure ofabout 100 to 125 p.'s.i.,rotation of the vessel being continued for a period of about thirtyminutes -t o onehour. -Any incrustants remaining after the partial(qr-complete venting of the vessel are saponified or otherwisesolubi-lized in the alkaline treatment. The vessel is again vented andthefibers are removed from it.

The .pre-steamed, alkaline extracted, mass is next washed directly withwater, which also keeps the yields at' an economicallysound value. It isthen agitated to breakup fiber bundles and screened. Because of thepurity of the fiber j'at'this point, it is not necessary to have apreliminary chlorination step. Previously used processes requirestwo-stage bleaching, comprising a preliminary chlorination, followed bybleaching with other conventional bleaching agents, such as calcium orsodium hypochloriteyand then followed by a secondary alkaline extractionstep. 1 Such processes are expensive, from both standpoints of materialsused and yield. By contrast, in my;process, calcium or sodiumhypochlorite is the only required bleaching agent and'the resultingyield is'appreciablyhigher. The bleach is followed by'a conventionalwashing.

-Depending upon the type of, pulp to be obtained from the bagasse, thatis, for example, whether an acetate type pulp which can be used in themanufacture of cellulose acetate is desired or a pulp for themanufacture of viscose film or filaments, or cellulose nitrate, or apaper pulp, the

steam-hydrolysis step may be varied as to either pressure or time oftreatment or both.v In general, the longer the timeand thehigher thesteam pressure, the lower will be the pentosan content and the higherwill he the alpha cellulose content of the resulting pulp product.

Similarly, the alkaline extraction step may be varied 'with' respect tocaustic content, liquor ratio, steam pres-.

sure, and time, or all four of these factors, depending upon the desiredend use of'the product. I

"By theuse of my invention, several advantages are enjoyed. The use of arotary vessel etfectsan appreciable savingin'timeand in quantity of heatrequired. With =the'useof'a rotating vessel, a superior degree'ofuniform- -'-ity ofsproduct'is achieved. Elimination of any added acidveifects an economy inmaterials. The partial ventingor blow-otf of thevessel after the pre-hydrolysis treatment effects a steam distillationof the incrustants which because a washing cycle is eliminated,increases theyield of the process. The partial venting also saves anappreciable amount of time and of fuel, since, in the subsequentalkaline extraction step, it is not necessary to raise the steampressure up all the way from atmospheric pressure. Moreover, due to. theeliminationof any. added. acid, no washing is needed betweenthepre-"hydrolysis 'and the alkaline extraction steps. This means afurther saving of time and ahigher yield, since there isno loss ofmaterial in washing. The elimination ofi a preliminary Lchlorinationstep effects a further saving in time and materials. Finally, since thetreated material is of high purity, only a single-stage bleach isrequired, "further saving time and materials.

I claim:

1. A process for producing purified cellulose pulp from bagasseconsisting of agitating and treating bag'asse with steam under pressureof to 125,p.s.i. .for aperiodof thirty minutes to one hour, rapidlyrelieving thepressure to one-half or less than'half its highest value,adding'to the materials. 2 to 3 percent caustic solution intheproportionof 5 partssolution to 1 part bagasse, by weight,

then agitating and cooking thematerial with live :steam.

under pressureof 100 to psi. for a 'periodof thirty minutes toonehour.

.2. A processfor producing purified cellulosepulpl from bagasseconsisting of agitating. and treating 'bagasse with steam under pressureof 100m 125 p.s.i.v for aperiod of thirty. minutes to onehour, rapidlyand .only partially. relieving-the pressure down to 50.10 60 psi, adding.to the material under pressure a 2 to 3 percent caustic solution in theproportion of 5 parts solution to l part bagass e, by weight, thenagitatingand cooking the material with live steam under pressure off-100to 125 .p.s.i. for. a period of thirty minutes to one hour.

References Cited in the file of thispatent" UNITEDSTATES PATENTS 109,742Keen "Nov. 29, 1870 117,683 Riddell Aug.l 1, 1871 811,419 'Manns "Jan.30, 1906 1,235,220 Marsden July 31, 1917 1,679,441 Nanji Aug. 7, 19281,729,772 Forsyth Oct.' 1,. 1929 1,739,683 Lucas .4 Dec. 17,19291,782,869 De La Roza Nov.,25, 1930 1,813,184 McQuiston et al. ..-'July7, 1931 1,831,032 Richter Nov. 10, 1931 1,931,933 Nicoll .Oct. 24, 19331,993,148 De Cew Mar. 5, 1935 2,049,676 Tomlinson Q. Aug. 4, 19362,161,763 Jones Jnne6, 1939 2,530,244 Jensen Nov. 14, 1950 2 ,560,638Dreyfus July..17, 1951 2,583,994 Briggs Jan. 29,. 1952 2,640,774 Ross etal. June 2 1953 OTHER REFERENCES

1. A PROCESS FOR PRODUCING PURIFIED CELLULOSE PULP FROM BAGASSECONSISTING OF AGITATING AND TREATING BAGASSE WITH STEAM UNDER PRESSUREOF 100 TO 125 P.S.I. FOR A PERIOD OF THIRTY MINUTES TO ONE HOUR, RAPIDLYRELIEVING THE PRESSURE TO ONE-HALF OR LESS THAN HALF ITS HIGHEST VALUE,ADDING TO THE MATERIAL A 2 TO 3 PERCENT CAUSTIC SOLUTION IN THEPROPORTION OF 5 PARTS SOLUTION TO 1 PART BAGASSE, BY WEIGHT, THENAGITATING AND COOKING THE MATERIAL WITH LIVE STEAM UNDER PRESSURE OF 100TO 125 P.S.I. FOR A PERIOD OF THIRTY MINUTES TO ONE HOUR.